A number of mechanical machining processes exist, where flaws can occur on the surfaces of workpieces and which cannot be detected at all or only with great effort, in spite of the fact that such flaws can result in final destruction or failure if the flawed workpieces are used for long periods. Typical examples are, for instance, heat checks and grinding checks in workpieces finish-machined by grinders, such as shafts, gear wheels or the like. Flaws which do arise can have different reasons or origins. They can be caused by workpiece tolerances, by positioning errors, by differing workpiece hardness and naturally by the condition of the tool bit, for instance by the condition of the grinding disc.
Such work processes are automated precisely in mass production, which entails that basically each machined workpiece must be subsequently inspected, in order to avoid later failure of the workpieces due to these machining defects, or in order from the start to eliminate such defective workpieces. Such an inspection is naturally very expensive.